Adjustable-Rate Mortgage Calculator
See how your payment and balance change as an adjustable rate resets, and how bad it could get if every cap is hit.
Quick answer
An adjustable-rate mortgage has a fixed starting rate that later resets to index plus margin, limited by periodic caps, a lifetime cap and a floor. The payment is recalculated at each reset on the remaining balance and term.
Adjustable-Rate Mortgage Calculator
Use a positive number to test rising rates.
Initial Payment
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Highest Payment (Expected)
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Highest Payment (Worst Case)
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Total Interest (Expected)
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Total Interest (Worst Case)
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Interest if Fixed at Initial Rate
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Year-by-Year Path (end of year)
| Year | Expected rate | Expected payment (₹) | Expected balance (₹) | Worst rate | Worst payment (₹) | Worst balance (₹) |
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Assumptions & method
- During the fixed period the rate equals the initial rate. Resets then occur every adjustment period, starting right after the fixed period ends.
- Target rate at a reset = expected index (plus the yearly change entered) + margin. The new rate is that target limited to ± the periodic cap from the current rate, then to at most initial rate + lifetime cap, then to at least the floor.
- Worst case: every reset rises by the full periodic cap until it reaches initial rate + lifetime cap. This is a stress test, not a forecast.
- After each reset the payment is recalculated: P × r × (1 + r)^m ÷ ((1 + r)^m − 1), with P the current balance, r = annual rate ÷ 12 and m the months left.
- The same periodic cap is applied to the first reset. Some contracts use a different first-reset cap; check your loan terms.
- Not included: taxes, insurance, fees, interest-only periods, negative amortisation, conversion options or extra payments.
Results are estimates based on the figures you enter. They are not guarantees and not financial advice.
Reading an adjustable-rate mortgage
An adjustable-rate mortgage starts with a fixed rate for a set number of years, then the rate follows an index plus a margin at each reset. Caps limit how fast and how far the rate can climb, and a floor sets the lowest rate. After every reset the payment is recalculated from the balance, the new rate and the months left, so a higher rate means a higher payment. This calculator builds two month-by-month paths: one using the index you expect, and a stress path where every reset rises by the full periodic cap until the lifetime cap is reached.